Demand paging in Operating Systems - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the sentence to describe demand paging.

Operating Systems

Demand paging loads a page into memory only when it is [1].

Drag options to blanks, or click blank then click option'

Areferenced

Bcreated

Cdeleted

Dwritten

Attempts:

3 left

💡 Hint

Common Mistakes

Assuming all pages are loaded at process start.

Demand paging means pages are loaded into memory only when they are actually referenced (used) by a process.

2fill in blank

medium

Complete the sentence to explain what causes a page fault.

Operating Systems

A page fault occurs when a process tries to access a page that is not currently [1] in memory.

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Aloaded

Bdeleted

Ccreated

Dstored

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing page fault with process crash.

A page fault happens when the page needed is not loaded in physical memory, so the system must load it from disk.

3fill in blank

hard

Fix the error in the statement about demand paging.

Operating Systems

Demand paging loads pages of a process into memory on [1].

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Aruntime

Bstart

Conce

Ddemand

Attempts:

3 left

💡 Hint

Common Mistakes

Thinking all pages load at process start.

Demand paging loads pages only when they are demanded (needed), not all at once.

4fill in blank

hard

Fill both blanks to complete the demand paging process description.

Operating Systems

When a page fault occurs, the operating system [1] the page from [2] into memory.

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Aloads

Bdeletes

Cdisk

Dcache

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing cache with disk.

On a page fault, the OS loads the needed page from disk into memory.

5fill in blank

hard

Fill all three blanks to describe the page replacement step in demand paging.

Operating Systems

If memory is full, the OS [1] a page using a [2] algorithm and then [3] the new page.

Drag options to blanks, or click blank then click option'

Aremoves

BFIFO

Cloads

Dcreates

Attempts:

3 left

💡 Hint

Common Mistakes

Thinking the OS creates pages instead of loading them.

When memory is full, the OS removes a page using a replacement algorithm like FIFO, then loads the new page.

Practice

1. What is the main purpose of demand paging in operating systems?

easy

A. To load pages into memory only when they are needed

B. To load all program pages into memory before execution

C. To increase the size of physical memory

D. To prevent any page faults during program execution

Solution

1. Step 1: Understand demand paging concept

   Demand paging means loading pages only when the program tries to use them, not before.

2. Step 2: Compare options with concept

   To load pages into memory only when they are needed matches this idea, while others describe different or incorrect behaviors.

3. Final Answer:

   To load pages into memory only when they are needed -> Option A

4. Quick Check:

   Demand paging = load pages on demand [OK]

Hint: Demand paging loads pages only when accessed [OK]

Common Mistakes:

• Thinking all pages load before execution
• Confusing demand paging with increasing memory size
• Assuming demand paging prevents all page faults

2. Which of the following is the correct description of a page fault in demand paging?

easy

A. When all pages are loaded into memory at once

B. When the CPU finishes executing all instructions

C. When the operating system shuts down

D. When a program tries to access a page not currently in memory

Solution

1. Step 1: Define page fault in demand paging

   A page fault occurs when a program accesses a page that is not in physical memory.

2. Step 2: Match definition with options

   When a program tries to access a page not currently in memory correctly describes this event; others describe unrelated events.

3. Final Answer:

   When a program tries to access a page not currently in memory -> Option D

4. Quick Check:

   Page fault = access missing page [OK]

Hint: Page fault happens on missing page access [OK]

Common Mistakes:

• Confusing page fault with program completion
• Thinking page fault happens during shutdown
• Believing page fault means all pages loaded

3. Consider a system using demand paging. If a program accesses pages in this order: 2, 4, 2, 5, 4, which pages cause page faults assuming none are initially in memory?

medium

A. No page faults occur because pages are preloaded

B. Pages 2, 4, and 5 cause page faults

C. Pages 2 and 5 cause page faults, but not 4

D. Only page 2 causes a page fault

Solution

1. Step 1: Identify initial memory state and page accesses

   No pages are in memory initially. Access order is 2, 4, 2, 5, 4.

2. Step 2: Determine which accesses cause page faults

   First access to page 2 causes a fault (not in memory). Then page 4 causes a fault. The second access to page 2 is in memory, no fault. Access to page 5 causes a fault. Last access to page 4 is in memory, no fault.

3. Final Answer:

   Pages 2, 4, and 5 cause page faults -> Option B

4. Quick Check:

   First access to new pages = page fault [OK]

Hint: First access to each new page causes fault [OK]

Common Mistakes:

• Assuming repeated pages cause faults
• Thinking pages preload automatically
• Ignoring initial empty memory state

4. A system using demand paging is experiencing frequent page faults. Which of the following could be a likely cause?

medium

A. The program accesses many pages not yet loaded

B. The CPU clock speed is too high

C. The hard disk is disconnected

D. The program is very small and fits in memory

Solution

1. Step 1: Understand causes of frequent page faults

   Frequent page faults happen when a program accesses many pages not currently in memory.

2. Step 2: Evaluate options for likely cause

   The program accesses many pages not yet loaded matches this cause. CPU speed or disk disconnection do not directly cause page faults. A small program fitting in memory would cause fewer faults.

3. Final Answer:

   The program accesses many pages not yet loaded -> Option A

4. Quick Check:

   Many new page accesses = frequent faults [OK]

Hint: Many new pages accessed cause faults [OK]

Common Mistakes:

• Blaming CPU speed for page faults
• Confusing hardware issues with paging faults
• Assuming small programs cause many faults

5. In a demand paging system, if the page replacement algorithm always removes the page that was least recently used, what is the main benefit of this approach?

hard

A. It increases the total number of pages in memory

B. It prevents any page faults from occurring

C. It reduces the number of page faults by keeping frequently used pages in memory

D. It loads all pages into memory before execution

Solution

1. Step 1: Understand least recently used (LRU) page replacement

   LRU removes the page not used for the longest time, keeping frequently used pages in memory.

2. Step 2: Identify benefit of LRU in demand paging

   This reduces page faults by avoiding removal of pages likely to be used soon.

3. Final Answer:

   It reduces the number of page faults by keeping frequently used pages in memory -> Option C

4. Quick Check:

   LRU keeps frequent pages, reduces faults [OK]

Hint: LRU keeps frequent pages, lowers faults [OK]

Common Mistakes:

• Thinking LRU increases memory size
• Believing LRU prevents all faults
• Confusing LRU with preloading all pages